Move Allergies API into the core platform

The allergies API which we have in the module https://github.com/openmrs/openmrs-module-allergyapi needs to be moved into the core platform.
This requires moving java files, hibernate mapping files, liquibase changesets, from the module to core.
Classes in "org.openmrs.module.allergyapi" go to "org.openmrs"
Those in 'org.openmrs.module.allergyapi.api" go to "org.openmrs.api"
Then from "org.openmrs.module.allergyapi.api.db" to "org.openmrs.api.db"
From "org.openmrs.module.allergyapi.api.db.hibernate" to "org.openmrs.api.db.hibernate"
From "org.openmrs.module.allergyapi.api.impl" to "org.openmrs.api.impl"

Move classes in org.openmrs.module.allergyapi.resource to the REST Web Services module: https://github.com/openmrs/openmrs-module-webservices.rest

Changesets in liquibase.xml go to liquibase-update-to-latest.xml

The global properties in config.xml go to org.openmrs.util.OpenmrsConstants

Remember to also move the unit tests.

When done with the above, ensure that mvn clean install runs successfully and that you can run the web application and login.
After doing all the above, if the reference application was running on master, you would try run it without the allergies-api module and see if all is well.